Workpiece thickness control apparatus



May 14, 1963 J. w. WALLACE ETAL 3,089,365

i WORKPIECE THICKNESS CONTROL APPARATUS Filed May 23, 1960 en J N l IJJc) m 2 A (D E 0) i q- Z E q- LL E ZJ O o U7 fl 8 FW' A II- 1 VW v a; cuE g a 4 9 (D 1 D b L 9 u l 2 i 2 .2. 2 2 4 E U) o g O -a O \,r Q g u) Q& o V N l 3 D" :l x 2 u" z o S2 w g O I o l v c m g (Lr) o r9 9| n mf J@E T/ o o n E 8 I0 WITNESSES INVENTORS @f John W. Wallace ond i 4, PoulE. Jacobs j BYMm/M ATTORNEY Pennsylvania Filed May 23, 1960, Ser. No.30,937 Claims. (Cl. 80-56) The present invention relates in general toworkpiece thickness control apparatus and more particularly to controlapparatus for a strip rolling mill or the like wherein the rolled actualthickness of the workpiece or strip is compared to a reference desiredthickness and the resulting error is provided as a signal and utilizedfor correcting the rolled thickness of the workpiece.

It is an object of the present invention to provide improved workpiecethickness control apparatus operative to better control a relativelyslow operating rolling mill such as a rolling mill operating below or inthe order of 2000 ft./min.

lt is a different object of the present invention to provide improvedworkpiece thickness control apparatus that is more stable in itsoperation, and is substantially static to thereby require lessmaintenance and repair, and is operative only when a thickness errorabove a predetermined value is present.

It is an additional object of the present invention to provide improvedworkpiece thickness control apparatus that is primarily operative assubstantially static thickness or gauge control apparatus in thatworkpiece tension correction relative to a rolling mill is usedpredominately, and only in the event of a predetermined or larger amountof thickness error is the nonstatic screwdown control of the rollingmill utilized to correct for the larger thickness errors.

These and other objects and advantages of the present invention willbecome apparent in View of the following description, taken inconjunction with the drawing, wherein: a schematic showing is made ofthe control apparatus in accordance with the teachings of the presentinvention.

ln the drawing there is shown a rolling mill including an upper rollerand a lower roller operative with a strip 12 of metal which passesthrough the rolling mill 10 from an input reel 14 to a windup reel 16. Astrip thickness measuring gauge 18 of the X-ray type for example isoperative to provide an youtput lsignal to an amplifier device 2G whichoutput signal corresponds to the difference between the actual measuredthickness of the strip 12 and a predetermined reference or desiredthickness for the strip 12. The output signal from the amplifier 20 issupplied to an input of a signal gate device 22 which is per se wellknown in the prior art and is operative to pass the error signal whenthe gate device is open and to block the passage of the error signalwhen the gate device is closed.

When the gate device 22 is opened as will be later described, the errorsignal is supplied to an integrating circuit 24, which could be, forexample, a motor operated rheostat or the like, and which provides anoutput error signal through an amplier 26 to a strip tension control 28operative with a motor 30 which runs the input or unwind reel 14. Inthis regard the strip tension control 28 may be a well known magneticamplifier type of variable voltage motor control, for example, with theerror signal from the amplifier 26 being supplied to a control windingof a magnetic amplifier for thereby varying the operative speed of themotor 30 in accordance with the value of the control signal supplied bythe amplifier 26. In this way the tension of the strip 12 between theunwind reel 14 and the rolling mill 10 is varied for the purpose ofnited States Patent raice varying the output thickness of the stripleaving the rolling mill lll.

The output signal from the amplifier 20 is also supplied to a signalvoltage sensing device 40. In this regard, the voltage sensing device 40is operative not to provide an output signal until the error signalreceived by the amplilier 20 reaches a predetermined value. In otherwords for values of the error signal below this predetermined minimumvalue, the voltage sensing device 40 does not provide an output signal.However, for values of the error signal supplied by the amplifier 20above this predetermined minimum value, such an output signal will beprovided. The operation of the gate circuit 40 in this regard is wellknown in the prior art. For example, a d-iode `bridge circuit having aback bias voltage across it will not pass an applied input signal of avalue less than said bias voltage.

lf desired, the voltage sensing or detecting device 40 may include aliip-flop circuit, such that it provides a binary type of output signal,either a zero value when the error signal supplied by the amplifier 26-is below the desired predetermined value or a unit value output signalwhen the error signal supplied by the ampliiier 20 is above thatpredetermined Value.

The output signal from the voltage sensing device 48 is operative toopen the gate device 22 through the illustrated NOR logic circuitry fora predetermined time interval as determined by the ON timer 46. Theoperation of the ON timer 46, when it stops its timing operation after aprovided ON time period, causes the OFF timer 48 to begin its timingoperation and to hold the gate device 22 in its closed state ofoperation for an OFF time interval dependent -upon the operating speedof the rolling mill 10 as sensed through a pulse source 5t) operativewith the mill motor 52.

lf desired a conventional tachometer may be provided to be operativewith the mill mo-tor 52 for providing an analog signal having a valueproportional to mill speed. Then the OFF timer 48 would be operative inresponse to the latter analog signal to provide an OFF time intervalinversely proportional to the value of this signal, such that the OFFtime interval would be or" shorter duration for a faster operating milland longer duration for a slower operating rolling mill.

The pulse source 56 provides output pulses to the OFF timer 48 at afrequency proportional to the operating speed of the rollingmill 10,such that after a predetermined number of pulses have been received bythe OFF timer 48, corresponding to a predetermined length of strippassing through the rolling mill 1t) and thereby compensating for thetransport time delay necessitated by the remote physical position of thethickness gauge 18 relative to the rolling mill 10, the OFF timer 48again allows a thickness correction operation to be made.

lt lsould be noted that the output signal from the integrating circuit24 is effectively the error control signal supplied to the strip tensioncontrol 28. If this thickness correction or error signal becomes greater4than a predetermined magnitude such that there is a likelihood ofendangering the breakage of the strip 12, for example, due to anexcessive strip tension `being required to effect the desired errorcorrection, then another voltage sensing device 60 is operative to allowthis error signal to p-ass to an input of an `automatic s-crewdownjogging control circuit 62, to cause the screwdo-wn motor control 68 tooperate in the proper direction as `determined by the signal from theamplifier for causing the serewdown motor 70 to vary the spacing betweenthe upper and lower roller members of the rolling mill 10.

The automatic jogging control `612 can be operative to effect periodicand timed changes in the spacing of the roller members of the rollingmill lll -for correcting any d strip thickness error. The time period ofthe changes can be controlled by the operating speed of the rolling mill10, such as taught in copending patent application Serial No. 17,983,filed March 28, 1960. and entitled Motor Control Apparatus, by the sameinventor and assigned to the same assignee. The error signal `from theamplifier 2t) causes the screwdown motor 70 to correct the thicknesserror, whenever the error signal has a predetermined value large enoughto be sensed by the voltage sensing device 60. The output signal fromthe voltage sensing device 60 can be utilized, for example, to energizea relay for controlling the passage of `the error signal from theamplier 20 to the screwdown motor control 68.

The present control apparatus is operative to provide a relatively fasttension gauge control that is applicable to particularly slow speedmills that operate with a strip speed in the order of 2000 t./min. orbelow. The workpiece thickness or gauge error signal is obtained fromthe thickness gauge 18 and is supplied to a preamplifier 20; The outputof the preamplifier 20 feeds the gate device 22 which is operative toeither supply the preamplifier output signal to the integrator circuit24 or block the passage of the preamplifier output signal. Theintegrator circuit 24 is operative to provide an error correction signalinto the strip tension control 23 for the unwind reel 14 and its motor30 through the power or output amplifier 26 to cause a change in thestrip tension between the unwind reel 14 and the rolling mill 10 in aproper direction that will reduce the workpiece thickness or gaugeerror.

The integrating circuit 24 is allowed to receive the output signal fromthe preamplifier 20 only if a predetermined and minimum thickness errorexists as determined by the voltage level sensing device 40 connectedbetween the output of the preamplifier device 20 and the provided NORlogic control circuitry. The device 40 in this regard is operative as avoltage level detector and includes a binary signal providing circuitsuch as a iiip-iiop or the like. The output signal from the voltagesensing device 40 has a one value in a binary sense until the errorsignal from the out-put of the preamplifier 20 exceeds the predeterminedvoltage sensing or `operating signal level of the device 40. If theerror signal received from the preamplifier 20 is greater than thelatter voltage sensing level, there is provided a zero value outputsignal to the NOR logic device 70 and the NOR device 72 within thetiming circuit 7'3.

The operation of a NOR logic device per se is believed to be well knownto persons skilled in this art. A NOR logic device provides a unit valueoutput signal until at least one of its inputs receives a unit valueinput signal, in which case the NOR logic device provides a zero valueoutput signal.

Thusly, when the voltage sensing device 40 provides the zero valueoutput signal, the NOR device 70 provides a unit value output signal.This allows the NOR device 74 to provide a zero value output signal. Thezero value output signal from the NOR device 74 causes the NOR device 72of the dip-flop circuit 75 to have a unit value output signal. The zerovalue signal of the NOR device 74 causes the NOR device 76 to have aunit value output signal since its second input as energized by theoutput of the ON timer is now also energized by a zero value inputsignal. The unit value output signal from the NOR device 76 causes thegate device to open and thereby allows the passage of the error signalfrom the output of the preampliier 20 to the integrating circuit 24. Thezero value output signal from the NOR device starts the operation of theON timer 46. After a predetermined ON time interval as initially set onfor the ON timer 46, the ON timer provides a unit value output signalwhich is supplied to an input of the NOR device 76 to thereby terminateits unit value output signal and thusly close the gate device 22.

'Ihe unit value output signal from the ON timer 46 also causes the NORdevice 72 to have a zero value output signal which starts the' OFF timer48 to provide a zero value output signal and begin counting pulsesreceived from the pulse source 5). The OFF timer 48 provides a unitvalue output signal until its input is energized by the NOR device 72providing a unit value output signal. After a predetermined number ofpulses have been received from the pulse source 5G and counted by theOFF timer 48, it again provides a unit value output signal to an inputof the NOR device 78. The zero value control signal from the OFF timer48 causes the NOR device 78 to have a unit value output signal to inturn cause the NOR device 70 to have a zero value output signal and theNOR device 74 to have a unit value output signal to further block theNOR device 76. Note that the unit value output signal from the ON timer46 causes the NOR device 76 to have a zero value output signal which isoperative to block or close the gate device 22.

Thusly, it will be seen that the gate device 22 was in this manneropened for a time period determined by the ON timer 46 providing a zerovalue output signal and further the gate device 22 is held closed for atime period determined by the OFF timer 48. The OFF timer 48 isresponsive to the pulses received from the pulse source for holding thegate device 22 closed through the operation of the NOR devices 78, 70,74 and 76 for a time period in accordance with the operating speed ofthe rolling mill 10 and thereby the movement of the strip 12. ln thismanner any correction made in the thickness or gauge of the strip 12 byvarying the tension between the unwind reel 14 and the rolling mill 10would have enough time to physically move from the rolling mill 10 tothe subsequent positioned thickness gauge 18 for measurement before anadditional error correction is made.

The unit signal from the OFF timer 48 causes the NOR device 78 to have azero output signal, and this in turn unblocks and allows the NOR device70 to respond to any zero signal supplied by the voltage sensing device40.

The ON timer 46 and the OFF timer 48 are per se well known devicesreadily available to persons skilled in this art.

If the error signal supplied by the amplifier 20 dccreases below thepredetermined voltage sensing level of the device 40, a unit valuesignal that is operative to block the timer circuit 73 is supplied to aninput of each of the NOR devices 70 and 72. This causes the NOR device70 to provide a zero output signal and the NOR device 74 a unit outputsignal, since the NOR device 72 is now supplying a zero signal to thesecond input of the NOR device 74. The unit signal from the NOR device74 blocks the gate device 22 through the NOR device 76 and furtherresets the ON timer 46. The NOR device 72 now provides a zero signal toreset the OFF` timer 48.

The control apparatus as shown in the figure provides a correctionproportional to the actual thickness error and which allows a maximumrate of correction to be used. The rate of correction of a given erroris determined by the integration constant of the integrating circuit 24and the ON time of the ON timer 46. The ON time is set to be onepreselected transport time period as determined by the known practicalrate of movement of the strip 12 between the rolling mill 10 and thethickness gauge 18 or less. The integration constant is set to correctas precisely as is practical the total error in one ON time period, andthe OFF timer 48 holds the circuit from resetting the ON timer until onetransport time period is over. At that time the ON timer is reset andready for another correction cycle if necessary.

Several correction operations are possible depending upon the magnitudeof the thickness errors existing. However, the integrator circuit 24will probably reach an excessive error correction limit now and then inthe course of its operation. When it does reach such an cxcessive limitthe voltage detector device 60 provides an output signal to permit thescrewdown gauge control to be energized and to function normally asthough no strip tension control were also being applied. Thusly, themajority of required thickness error corrections are made solely in asubstantially static manner without mechanical movement of the screwdownapparatus by varying the tension of the strip between the unwind reel 14and the rolling mill 10. However, the screwdown motor 70 can employedfor effecting the desired thickness corrections when needed. Theadvantage of varying the strip tension is that this is in eiect a staticcontrol system in that the unwind reel motor 30 is already operating andthe strip tension control 28 may be a static device in the form of avariable voltage magnetic amplier control. The screwdown motor 70 whenit operates to vary the spacing between the upper roller member and thelower roller member operates the mechanical screwdown and if this isdone too often excessive maintenance results and repairs becomenecessary. Thusly, the present control apparatus provides the desiredmaximum speed of response and accuracy of strip thickness errorcorrection while reducing the number of screwdown changes to au absoluteminimum.

Although the present invention has been described with a certain degreeof particularity, it should be understood that the present disclosurehas been made only by way of example and that numerous changes in thedetails of construction and the combination and arrangement of parts maybe resorted to Without departing from the scope andthe spirit of thepresent invention.

We claim as our invention:

1. `In strip thickness control apparatus for a rolling mill including astrip thickness error correction device, the combination of an errorsignal source operative with the strip for providing an error signalhaving a value in accordance with the strip thickness error, a signalgate device operative with said error signal source, signal integrationmeans connected between said signal gate device and the error correctiondevice for controlling the passage of the error signal to the errorcorrection device for the purpose of varying the thickness of the striprolled by said rolling mill in accordance with the integral of saiderror signal, a timing device operative with said gate device foropening the gate device for a predetermined time duration period, and asignal magnitude sensing device operative with said signal source andconnected to said timing device for controlling the operation of saidtiming device in accordance with the magnitude of said error signal andthereby the thickness error of said strip.

2. In strip thickness control apparatus for a rolling mill including astrip tension control device, the combination of an error signal sourceoperative with the strip for providing a strip thickness error signal, asignal gate device operative with said error signal source, signalintegration means connected between said signal gate device and thestrip tension control device for controlling the passage of apredetermined integral of the error signal to the tension control devicefor the purpose of varying the tension of the strip relative to saidrolling mill and thereby the thickness of the strip rolled by saidrolling mill, a timing device operative with said gate device foropening the gate device for a predetermined time duration period, and asignal magnitude sensing device operative with said signal source andconnected to said timing device for controlling the operation of saidtiming device in accordance with the magnitude of said error signal andthereby the thickness error of said strip.

3. In strip thickness control apparatus for a rolling mill including astrip tension control device, the combination of an error signal sourceoperative with the strip -for providing a strip thickness error signal,a signal gate device operative with said signal source, signalintegration means connected between said signal gate device and thestrip tension control device for controlling the supply of theintegrated error signal to the tension control device for the purpose ofvarying the tension of the strip and thereby the thickness of the striprolled by said rolling mill, a timing device responsive to the movementot the strip and operative with said gate device for opening the gatedevice for a time duration period dependent upon tlie rate of movementof the strip, and a signal magnitude sensing device operative with saidsignal source and connected to said timing device for controlling theoperation of said timing device in accordance with the magnitude of saiderror signal and thereby the thickness error of said strip. p

4. In strip thickness control apparatus for a rolling mill including astrip tension control device, the com bination of an error signal sourceoperative with the strip for providing a strip thickness error signal, asignal gate device and signal integration means connected between saidsignal source and the strip tension control device for controlling thepassage of an error correction signal to the tension control device fromsaid signal integration means for the purpose of varying the tension ofthe strip and thereby the thickness of the strip rolled by said rollingmill, a control signal source operative with said strip for providing acontrol signal having a predetermined characteristic proportional to themovement speed of the strip, a timing device responsive to saidcharacteristic of said control signal and operative with said gatedevice for opening the gate device for a controlled time durationperiod, and a signal magnitude sensing device operative with said signalsource and connected to said timing device for controlling the operationof said timing device in accordance with the magnitude of said errorsignal and thereby the thickness error of said strip.

5. In strip thickness control apparatus for a strip rolling millincluding a strip tension control device and a screwdown control device,the combination of an error signal source operative with the strip forproviding a strip thickness error signal having a value in accordancewith the dilerence between the actual strip thickness and apredetermined reference strip thickness, a signal gate device and asignal integration circuit connected between said signal source and thestrip tension control device -for controlling the passage of theintegrated error signal to the tension control device for the purpose ofvarying the l tension of the strip by an amount in accordance with themagnitude of said error signal, a timing device operative with said gatedevice for opening the gate device for a predetermined time durationperiod, a lirst signal magnitude sensing device operative with saidsignal source and connected to said timing device for controlling theoperation of said timing device in accordance with a first magnitude ofsaid error signal and thereby the thickness error of said strip, and asecond signal magnitude sensing device operative with said signal sourceand connected to control said screwdown control device for controllingthe operation of said screwdown control device in accordance with asecond magnitude of said error signal, with saiid second magnitude beinggreater than said rst magnitu e.

References Cited in the iile of this patent UNITED STATES PATENTS2,264,096 Mohler Nov. 25, 1941 2,767,604 Whalen Oct. 23, 1956 2,909,717Hulls et al. Oct. 29, 1959 '2,933,626 Giboney et al Apr. 19, 19603,015,974 Orbom et al.V Jan. 9, 1962 OTHER REFERENCES non and steelEngineer, August i956, pp, 132-140. Automation, March 1956, pp. 52-57.Iron and Steel Engineer, July 1958, pp. 124-132.

2. IN STRIP THICKNESS CONTROL APPARATUS FOR A ROLLING MILL INCLUDING ASTRIP TENSION CONTROL DEVICE, THE COMBINATION OF AN ERROR SIGNAL SOURCEOPERATIVE WITH THE STRIP FOR PROVIDING A STRIP THICKNESS ERROR SIGNAL, ASIGNAL GATE DEVICE OPERATIVE WITH SAID ERROR SIGNAL SOURCE, SIGNALINTEGRATION MEANS CONNECTED BETWEEN SAID SIGNAL GATE DEVICE AND THESTRIP TENSION CONTROL DEVICE FOR CONTROLLING THE PASSAGE OF APREDETERMINED INTEGRAL OF THE ERROR SIGNAL TO THE TENSION CONTROL DEVICEFOR THE PURPOSE OF VARYING THE TENSION OF THE STRIP RELATIVE TO SAIDROLLING MILL AND THEREBY THE THICKNESS OF THE STRIP ROLLED BY SAIDROLLING MILL, A TIMING DEVICE OPERATIVE WITH SAID GATE DEVICE FOROPENING THE GATE DEVICE FOR A PREDETERMINED TIME DURATION PERIOD, AND ASIGNAL MAGNITUDE SENSING DEVICE OPERATIVE WITH SAID SIGNAL SOURCE ANDCONNECTED TO SAID TIMING DEVICE FOR CONTROLLING THE OPERATION OF SAIDTIMING DEVICE IN ACCORDANCE WITH THE MAGNITUDE OF SAID ERROR SIGNAL ANDTHEREBY THE THICKNESS ERROR OF SAID STRIP.